1. Field of the Invention
The present invention relates to a strain gauge strip, of the type made of semiconductor material, which can be mechanically applied to a sensitive element subject to deformation. The present invention further relates to applications of said strain gauge strip, in particular to electric strain gauge sensitive elements, measuring instruments and related calibration procedures, pressure scales and transducers. The invention also relates to a method for manufacturing said sensitive element.
2. Description of Related Art
It is a known fact that strain gauge strips are widely used to measure dynamic deformations and, indirectly, to measure forces such as weights, pressures and other forces causing said deformations in a special support. For this purpose they are electrically assembled as a Wheatstone bridge to limit the influence of variations in temperature in the strain gauge strips. The Wheatstone bridge is excited, at two opposite ends, by a reference voltage; the deformation causes a variation in the length of strain gauge strips, with a corresponding variation in the associated electrical resistance value. On the other opposite ends of the bridge a signal is detected, consisting in an electrical voltage substantially corresponding to the deformation that has occurred. This signal represents the force that has caused deformation of the sensitive element.
However, known strips are subject to certain problems, which considerably limit the extent to which they are used. In particular, they generate a signal that does not exceed 2-3 mV/V with respect to the excitation voltage. Furthermore, the electrical resistance they provide is too low, resulting in a considerable dissipation of energy, and they have to be assembled in complex lay-outs that foresee a number of resistors for calibration and control of the influence of temperature. In order to avoid the above problems at least partially, strain gauge strips based on semiconductor materials, e.g. silicon, have been provided, which generally make it possible to obtain a greater output signal. This type of strip, although it is more sensitive, is considerably subject to influences in temperature, so that strips of this kind can be used in extremely controlled conditions, for example in physics laboratories and the like.
Furthermore, a strain gauge strip based on known semiconductor material can be used to measure deformations that fall within very restricted ranges. The most important types of commercial use, for example those connected with determination of weight in the retail sale of goods and products, are therefore precluded for this type of strain gauge strip, as in any other form of use out of doors or in environments that are not thermally conditioned.
The technical problem at the base of the present invention is that of providing a strain gauge strip that is capable of overcoming the drawbacks mentioned with reference to the prior art. This problem is overcome by a strain gauge strip as described below.
The main advantage of the strain gauge strip according to the present invention lies in the fact that it gives excellent performance in terms of precision and sensitivity, without suffering the influence of temperature and for a wide range of deformations, well suited to commercial use.